1. Field of the Invention
The field of the invention is the art of walk-through ladders, inclusive of fixed ladders, which are permanently attached to a structure such as a building.
2. Description of the Related Art
A so called "through" ladder requires a climber getting off at the top to step through the ladder in order to reach a landing. "Walk-through" fixed ladders are also well known; they typically include a flared section at the top through which the climber walks. See the prior art device in FIGS. 8 and 9 which will be more fully described below.
Fall protection is mandatory through OSHA regulations on fixed ladders over 20 feet tall in general industry and 24 feet tall in construction. The addition of a post or a rail in the center or at the side of the ladder creates an impediment to circumvent so an outside fitting is safer. Ladders could be upgraded by having climbing safety devices installed as extra protection. About half of the ladders in use are less than 20 feet high so such improvements would serve the purpose well if no fall protection exists for these ladders.
One problem with the flared walk-through ladder is that the climber routinely holds a side rail while descending until the moment the flared section is reduced to 16 inches in width. Unless users observe the need to place the hands closer to the body in order to grasp the side rails or rungs on the main body of the ladder, a person will grasp at thin air and will be subject to a fall at that moment if he has transitioned his feet and assumed the location of the handhold by getting ready to release the other hand.
Moreover, when 21/2-3-inch width angle iron is used as the side rail, only a push-pull pinch grip can be made on the side rails and any fall at the walk-through portion of the ladder is likely to be catastrophic in its outcome. In fact, the ability to hold any vertical shape of the side rails sufficiently to regain balance is not possible. The problems with side rail holdings are several.
First, the hand slides down due to the weight of the body. Second, the force of arresting a free fall up to three feet, i.e. the length of the arm, is dynamic. From rope tests, it is known that the maximum force of a moving rope which can be held is 50 pounds and the least is approximately 10 pounds, both far below a person's body weight. These references are found in the ISFP Newsletter of October, 1996.
Third, a swing fall into the side of the ladder produces an impact of the body with the ladder since the body's center of gravity has to move eight inches from center to side because a ladder rung is 16 inches long. If a person is standing far over to the side, then a movement of 16 inches will occur with an even higher swing fall collision which further tends to destabilize the hand grip.
Fourth, some ladder side rails are impossible to encircle with the hand, e.g., three-inch angle irons or two-inch flange I-beams. Because these shapes cannot be encircled with the hand for a good grip, only a pinch grip can be used and no fall arrest is remotely possible. With two-inch or 21/2-inch widths, grips are possible but, due to the factors described above, the grip cannot become an effective grasp under foreseeable methods of climbing on these ladders and a catastrophe must necessarily follow, if the climber falls.
Fifth, the ground or surface below a fixed ladder is almost always unyielding, thus providing the maximum possible deceleration upon impact and therefore the greatest injury to a falling worker.
Sixth, ladders constitute the primary cause of injurious occupational falls based on current OSHA statistics. Since these statistics include portable ladders as well as fixed ladders, it is evident that a climber, who loses his balance on a ladder, needs all the help possible to maintain a grasp that can be reasonably effective if a foot were to slip at the most vulnerable transition points on the ladder.
All climbers eventually misstep no matter how well they are trained. Usually, the climber is preoccupied about achieving the purpose for which the ladder is climbed, not the actual climbing of the ladder. Therefore, exposure to fall hazards cannot be expected to be controlled effectively solely by training workers to climb ladders with the utmost attention to human factors and back-up safety features.
Typical of walk-through ladders in the prior art is the fixed ladder illustrated in FIGS. 8 and 9. A lower section of a walk-through ladder L is shown below a surface A which schematically represents a level to which a climber C is ascending from a lower surface G. The ladder L includes side rails 1 with a plurality of round foot rungs 2. By way of example, each rung 2 can be 16 inches long at a minimum and 3/4 to one inch in diameter. Each side rail 1 can be 21/2 inches wide by 33/8 inch to one-half inch in thickness or any size or shape which provides a power grip with materials, such as carbon steel or aluminum, being selected appropriately for the ladder length, usage and environment.
As best shown in FIG. 8, the ladder L at its top above the surface A flares outwardly to form a walk-through section W. The architecture of the walk-through section W may vary depending upon requirements. However, the walk-through section W has parallel vertical side rails 21 and 22 forming an opening O generally, in order to meet code requirements, spaced apart at a distance one from the other about 24 to 30 inches.
As it is also seen in FIG. 9, the walk-through opening O is minimally 31/2 feet in height. In this case, if the climber C is about 5'8" tall, the opening O may be about four feet high.
In FIG. 9, the climber C ascends the ladder L normally. As the climber C negotiates his way into and through the opening O, as indicated by arrows R, onto the surface A, the climber's feet may slip. The vertical side rails 21 and 22 of FIG. 8, regardless of shape or configuration, cannot be grasped without great risk of the climber's grip sliding and/or opening up, depending upon the nature of the slip. Furthermore, a free fall can develop from zero to twice the climber's arm length, resulting in an impact on any grip that the climber C may have. In addition, a swing to one side of the ladder L may result in an impact against the side rails 1 of the ladder L. Consequently, the climber's grip cannot be maintained and a hard fall to the surface C below usually occurs, resulting in serious injury or death.